OBC retrofit

Today I swapped out my old 6-button OBC for a 13-button one. The swap consisted of the 13-button OBC, wiring harness, and turn-signal stalk. The stalk was a pain in the butt, and quite honestly was the easiest part of the whole thing.

Putting the OBC in consists of disassembling pretty much your entire dash content, with the exception of the dash itself. All center switches were taken out/popped out, radio removed, steering wheel removed, instrument cluster removed, steering column cover removed, and a bit of my sanity removed.

The wiring harnesses are held together by clips that are kind of "built-in" the dash, kind of like the adhesive-backed things you could zip-tie things to. The only difference is that these plastic cable-holders are so old that they break. So, in essence, you can't reuse them, and I learned that the hardware when I tried to put back my instrument cluster.

The wire bundles are supposed to run along the top of where the cluster would be so that the cluster itself can actually fit into that tight space. I tried to shove the cluster in with the wires along the rear but the damned thing wouldn't go in. Since the cable-holders were broken, I couldn't reuse those in any way, including zip-tying the cables to parts of the holder. In the end, I wound up using velcro straps to wrap around the cable bundles and then another piece of sticky velcro lining the top of the space so I could stick the cable bundles on the velcro, holding the bundle up enough to allow the instrument cluster to slide in.

Anyway, I did test the OBC at point one and found that the brand new light bar that BavAuto sent me is non-functional. The OBC display doesn't light up at all, while the buttons do. I tried the light bar that came with the OBC and the one from BavAuto and neither worked.

Is there anything that could prevent the light bar from working? Is it really possible that both the old one (more probable) AND the new one (not so much) don't work?

Yes, my car is put back together so I will have to redo about half of the work at some other time, but before I do that, I want to order what I need so I don't EVER have to go through that hell again.

The coding plug - I looked up some coding plug part numbers that are supposed to be used for the different engine types. The guy I bought the OBC from said it was from an '87 325is. The part number on the OBC seemed to correspond to the plug used for an E30 M3, and I have a 325e. I seriously doubt it is from an M3, so my question is, would this plug work correctly for my car? I mean, the only difference that I know between the B27 and the B25 is the rev limit (and power obviously), so why would it require a different coding plug?

I did forget that the gas tank volume changed with later models, but I used an 87 325i as a donor, so it did not matter. It would only be slightly off. The electronics are vastly different from early B27 to the later Motronic of the B25. Initially I meant you can't use an M3 coding plug, but the 2.5i coding plug may be slightly off because the volume of fuel injected per ms of pulse width are different between the 2.5 and early 2.7 due to different injectors and fuel pressure. It may not be that far off, though.

I have never heard Botond drop so many F-bombs on the phone when he told me about this nightmare. I called him up to tell him I got a great deal on 330xi 17's and he is F-bombing this, F-bombing that. I hope it all works out man

I bought the correct coding plug from a recycler for $5 (10 years ago). I was told at the time that the plug I had was for a European model with a substantially bigger gas tank; suspicious story, but my Range calculation was badly wrong with the wrong plug.

Botond and waiting don't belong in the same sentence. He will drive to you to pick it up.

Thaaaaaaaat's right.

How long are we talking here? I want to get this thing up and running ASAP and will be contacting BavAuto first thing in the morning if my ohm test fails on the light bar (which BTW I still do not know what reading I'm looking for!). I really don't feel like rewiring my radio wiring a few more times so I'd really like to take care of all this in one shot...

If you're saying sometime this week so I could have it by Friday or Saturday at the latest, then sure I'll wait. Otherwise, I'm going to have to order one, though I'll keep the old one just in case I do my 2.7i swap. *just in case*. Saving money instead of spending it is a pain...

Also, I realized I have an extra "something" after the install. Does anyone know what this device is?

The part number on it is: 65 81 1 373 726
Realoem says relay, but what kind of relay? For what? Is it necessary?

Some of us have steady jobs, so we can't go tearing apart a parts car for a coding plug on the spur of the moment.
That box has two relays. One controls the tone for the black ice warning, and the other is for the coded driveaway protection. You don't need it, but without it you can't use the anti-theft feature that is built in to the 13 button OBC. There is a bit of the harness that you will also have to swap over by the computer.

You are just looking for a resistance below infinity, that is, you are checking to see if the filaments in light bulbs are intact. Another way to do it is to use a magnifying glass or 10x loupe to visually inspect the bulbs; you might be able to see a broken filament.

I measured the lightbar but I seriously doubt I was doing it right because I got a reading of less than an Ohm.

Neither the old or new bars have broken filaments upon visual inspection. I just don't get it!
I even went as far as to take out the circuit board with the bulbs and stick those in manually to make sure that there aren't "contact" issues with the pins inside the OBC. They plugged right in, nice and firm, and yet still no display illumination. Button illumination is fine though, but I made sure of that by putting in a known good bulb [wanted to put a new one but couldn't for the life of me get the old bulb out of the holder].

It sounds like the bulbs in the light bar check out okay: less than 1 ohm is good because it means there is a nice electrical connection from one terminal, through the bulbs, to the other terminal. Your light bar is probably fine.

This is bad news. That means that there is a problem somewhere in the OBC itself. It is likely not providing voltage to the light bar terminals. The light bulbs are not getting juice to light them up.

You next need to check the OBC: set the multimeter to measure DC volts and measure the voltage across the two OBC terminals for the light bar: it should show a voltage and probably 12v (may sure you don't have your dashboard lights fully dimmed). If it doesn't show a voltage, something is wrong in the OBC or in the power you are supplying to it (your harness connections).

If you do measure a voltage across the OBC terminals, that means that the problem is that simply the light bar and the OBC terminals are not making a good electrical connection. This would be good news because its easy to fix (clean the contacts, bend the contacts to make a better connection, etc).

Just an aside, the light bar gets more power with the headlights off so you can read it in sunlight, so you won't be getting anywhere close to 12V unless the headlights are off. I suspect the harness connections are good if the keypad light works.